Basic research is proposed involving the newly described immunosuppressive feline T-lymphotropic lentivirus (FTLV) reported by Pedersen et al. This application is designed to provide information on FTLV prevalence, transmission, immunosuppressive effects and variability among individual FTLV isolates, and it also covers development of reference reagents and an ELISA diagnostic test for FTLV infection. Our efficient, previously established, feline retrovirus referral program will be used to identify and collect FTLV infected cats from Seattle: cats diagnosed FTLV positive and with a documented history of immunosuppressive diseases that fit FTLV-associated immunodeficiency syndrome (FTLV- FAIDS). Lymphocytes from ten such cats will be used to culture FTLV-infected lymphocytes in vitro using recombinant interleukin 2 and co-culturing techniques. FTLVs isolated from culture supernatant's will be used as capture antigen to develop an ELISA for FTLV infection by detecting feline antibodies in exposed cats. FTLV production will also be studied in culture, and the virus isolates will be used to produce monoclonal antibodies (mabs) to individual and cross-reactive virus epitopes. At least 1000 feline sera samples will be analyzed for FTLV antibodies in order to determine the prevalence of FTLV exposure in the pet cat population. Five kittens will be naturally contact-exposed to an equivalent number of FTLV positive cats, and a further 5 kittens will be injected with blood donated from FTLV positive donors. These 20 cats will be studied at approximately 4 week intervals for at least 18 months to establish profiles for hematology, immune mechanisms, and blood chemistry. MAbs to normal feline T-cell subsets will be produced early in the project in order to aid the immunologic analysis. Finally, we will test blood samples form cooperative owners of FTLV positive pets and from normal volunteers in order to determine if FTLV exposed humans react serologically to this cat lentivirus.